What are the xovers for all your speakers?
DBII will remove embedded "ambiance" signals from your mains to distribute it to other speakers. If those speakers do not have the same configuration than your mains (especially if you are using you mains in a full-range or low xover), you might get quite a bit of signals now sent to your sub-woofer that were sent to your mains, especially from your central channel.
That could be an indication (if the difference is THAT big), that your sub-woofer might be configured too "hot" to match your mains only.
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E = MC2 = ((2M80 + VP180 + 4QS8)/(EP800 + EP500))^(ADA1500 x D2v)
Audiobytes! 2M22! 2VP150!